In the Navajo language, they are called BisTaHi – the badlands. Their name belies a subtle beauty. More than two-hundred million years ago, these lands were swamps and river flood plains bordering an equatorial Pangean sea. During the Pleistocene, the clay beds were exposed and the present topology first formed. The forces of erosion continue to sculpt the clay into barren landscapes whose colors derive from minerals and carbon. The bentonite clay is decomposed volcanic ash deposited during the Mesozoic era. It swells into a sticky plastic when wet. Saturated bentonite slumps and flows, creating rounded, deeply cut hills. The clay dries to a puffy, cracked consistency that easily becomes dust and erodes too rapidly to permit plants to grow and produce soil. Exposed throughout the badlands are now petrified woods and smoothed gravels that were deposited along the coastal Triassic flood plains.